It is possible to use a certificate generated using Codename One wizard on two different projects without having to generate a new one every time I change project?
Yes, you can. Generate the certificate once in your first project and then in your second project, go through the certificate wizard and when it asks if you want to generate new certificates, choose "no". Once complete, you'll then have to reference your certificates manually in the iOS settings.
I have a number of POC projects that I'm developing right now in hopes of porting my Android app over to codenameone, and I'm reusing the same certificates for all of them.